1. Field of the Invention
This invention relates generally to the use of radar coverage information derived from terrain elevation data in generating mosaic products of weather radar returns from multiple weather radars. The invention specifically describes the use of terrain-based radar coverage information in an algorithm for generating mosaic products (i.e., products that cover more than one radar coverage area) from composite reflectivity radar products generated by weather radars.
2. Background
Weather radar returns are often contaminated by non-meteorological artifacts present in the data that are unrelated to the primary observation objective of the radar, namely weather observations. For example, the United States Government operates a network of WSR-88D weather surveillance radars in the continental US, Alaska and Hawaii which provide real-time weather information. The data from these radars is frequently contaminated by returns that are of non-meteorological origin, for example: ground clutter returns, anomalous propagation (AP) returns caused by refraction of the radar beam in the atmosphere, RF interference returns, solar interference returns, spurious returns caused by degraded or failed radar signal processing components in the WSR-88D radars, returns from air-borne dust and insects, and other known and unknown anomalies. Mosaic generation algorithms that simply combine the returns from weather radars with overlapping coverage areas produce mosaic products which may contain significant non-meteorological content. There can be substantial economic or human costs attributable to inaccuracy over a mosaic region, especially where the mosaic is relied upon in aviation or ground based transportation decision-making. Therefore, producing mosaic products without significant non-meteorological content is an important goal.
The objective in designing a weather mosaic generation algorithm is to maximize suppression of non-meteorological returns and to minimize removal of valid weather returns. For many applications there can be a severe penalty for removing valid weather returns (for example, weather products used in air traffic control applications). Various algorithmic processes for generating mosaic products from multiple weather radars have been developed to identify and remove non-meteorological returns with varying levels of success. Some of the algorithmic approaches used in designing mosaic generation algorithms are:                1. Select data from closest radar.        2. Select data from radar with the best view (view can be based on terrain elevation information).        3. Assigning confidence levels to individual contributors (for example, a variety of range-based strategies are used for assigning confidence levels).        4. Compute confidence-based average of contributing radars.        5. Select highest confidence contributor.        6. Select highest supported contributor.        7. Using other types of data to validate radar returns (satellite images, weather model outputs, etc.).        
The invention describes a preferred embodiment set of algorithms that utilize terrain-based radar coverage information for generating weather mosaic products from WSR-88D composite reflectivity product data. They can be applied to other radar mosaic products as well, as one of ordinary skill in this area of endeavor will readily appreciate. Composite reflectivity radar products are generated by the WSR-88D radars by combining data at a given range/azimuth location with respect to the radar location from multiple elevation tilts that provide coverage within the elevation layer of interest (for example, surface to 18,000 meters). The radar coverage information used by this algorithm are radar-specific radar coverage maps which specify the minimum viewable elevation above mean sea level (MSL) for each radar product bin. The coverage maps have the same spatial resolution as the corresponding radar product data. The preferred techniques for generating radar coverage maps for composite reflectivity products from terrain elevation data are described in U.S. Pat. No. 6,771,207, incorporated herein in its entirety by this reference thereto.
It should be recognized that the teachings of this invention can apply to data from other types of weather radars, and to other types of weather radar products (single tilt base reflectivity product data, layer composite reflectivity product data, vertical integrated liquid (VIL) product data, etc.